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feat(flags): Match flags on rollout percentage (#45)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,161 @@ | ||
| use crate::flag_definitions::{FeatureFlag, FlagGroupType}; | ||
| use sha1::{Digest, Sha1}; | ||
| use std::fmt::Write; | ||
|
|
||
| #[derive(Debug, PartialEq, Eq)] | ||
| pub struct FeatureFlagMatch { | ||
| pub matches: bool, | ||
| pub variant: Option<String>, | ||
| //reason | ||
| //condition_index | ||
| //payload | ||
| } | ||
|
|
||
| // TODO: Rework FeatureFlagMatcher - python has a pretty awkward interface, where we pass in all flags, and then again | ||
| // the flag to match. I don't think there's any reason anymore to store the flags in the matcher, since we can just | ||
| // pass the flag to match directly to the get_match method. This will also make the matcher more stateless. | ||
| // Potentially, we could also make the matcher a long-lived object, with caching for group keys and such. | ||
| // It just takes in the flag and distinct_id and returns the match... | ||
| // Or, make this fully stateless | ||
| // and have a separate cache struct for caching group keys, cohort definitions, etc. - and check size, if we can keep it in memory | ||
| // for all teams. If not, we can have a LRU cache, or a cache that stores only the most recent N keys. | ||
| // But, this can be a future refactor, for now just focusing on getting the basic matcher working, write lots and lots of tests | ||
| // and then we can easily refactor stuff around. | ||
| #[derive(Debug)] | ||
| pub struct FeatureFlagMatcher { | ||
| // pub flags: Vec<FeatureFlag>, | ||
| pub distinct_id: String, | ||
| } | ||
|
|
||
| const LONG_SCALE: u64 = 0xfffffffffffffff; | ||
|
|
||
| impl FeatureFlagMatcher { | ||
| pub fn new(distinct_id: String) -> Self { | ||
| FeatureFlagMatcher { | ||
| // flags, | ||
| distinct_id, | ||
| } | ||
| } | ||
|
|
||
| pub fn get_match(&self, feature_flag: &FeatureFlag) -> FeatureFlagMatch { | ||
| if self.hashed_identifier(feature_flag).is_none() { | ||
| return FeatureFlagMatch { | ||
| matches: false, | ||
| variant: None, | ||
| }; | ||
| } | ||
|
|
||
| // TODO: super groups for early access | ||
| // TODO: Variant overrides condition sort | ||
|
|
||
| for (index, condition) in feature_flag.get_conditions().iter().enumerate() { | ||
| let (is_match, _evaluation_reason) = | ||
| self.is_condition_match(feature_flag, condition, index); | ||
|
|
||
| if is_match { | ||
| // TODO: This is a bit awkward, we should handle overrides only when variants exist. | ||
| let variant = match condition.variant.clone() { | ||
| Some(variant_override) => { | ||
| if feature_flag | ||
| .get_variants() | ||
| .iter() | ||
| .any(|v| v.key == variant_override) | ||
| { | ||
| Some(variant_override) | ||
| } else { | ||
| self.get_matching_variant(feature_flag) | ||
| } | ||
| } | ||
| None => self.get_matching_variant(feature_flag), | ||
| }; | ||
|
|
||
| // let payload = self.get_matching_payload(is_match, variant, feature_flag); | ||
| return FeatureFlagMatch { | ||
| matches: true, | ||
| variant, | ||
| }; | ||
| } | ||
| } | ||
| FeatureFlagMatch { | ||
| matches: false, | ||
| variant: None, | ||
| } | ||
| } | ||
|
|
||
| pub fn is_condition_match( | ||
| &self, | ||
| feature_flag: &FeatureFlag, | ||
| condition: &FlagGroupType, | ||
| _index: usize, | ||
| ) -> (bool, String) { | ||
| let rollout_percentage = condition.rollout_percentage.unwrap_or(100.0); | ||
| let mut condition_match = true; | ||
| if condition.properties.is_some() { | ||
| // TODO: Handle matching conditions | ||
| if !condition.properties.as_ref().unwrap().is_empty() { | ||
| condition_match = false; | ||
| } | ||
| } | ||
|
|
||
| if !condition_match { | ||
| return (false, "NO_CONDITION_MATCH".to_string()); | ||
| } else if rollout_percentage == 100.0 { | ||
| // TODO: Check floating point schenanigans if any | ||
| return (true, "CONDITION_MATCH".to_string()); | ||
| } | ||
|
|
||
| if self.get_hash(feature_flag, "") > (rollout_percentage / 100.0) { | ||
| return (false, "OUT_OF_ROLLOUT_BOUND".to_string()); | ||
| } | ||
|
|
||
| (true, "CONDITION_MATCH".to_string()) | ||
| } | ||
|
|
||
| pub fn hashed_identifier(&self, feature_flag: &FeatureFlag) -> Option<String> { | ||
| if feature_flag.get_group_type_index().is_none() { | ||
| // TODO: Use hash key overrides for experience continuity | ||
| Some(self.distinct_id.clone()) | ||
| } else { | ||
| // TODO: Handle getting group key | ||
| Some("".to_string()) | ||
| } | ||
| } | ||
|
|
||
| /// This function takes a identifier and a feature flag key and returns a float between 0 and 1. | ||
| /// Given the same identifier and key, it'll always return the same float. These floats are | ||
| /// uniformly distributed between 0 and 1, so if we want to show this feature to 20% of traffic | ||
| /// we can do _hash(key, identifier) < 0.2 | ||
| pub fn get_hash(&self, feature_flag: &FeatureFlag, salt: &str) -> f64 { | ||
| // check if hashed_identifier is None | ||
| let hashed_identifier = self | ||
| .hashed_identifier(feature_flag) | ||
| .expect("hashed_identifier is None when computing hash"); | ||
| let hash_key = format!("{}.{}{}", feature_flag.key, hashed_identifier, salt); | ||
| let mut hasher = Sha1::new(); | ||
| hasher.update(hash_key.as_bytes()); | ||
| let result = hasher.finalize(); | ||
| // :TRICKY: Convert the first 15 characters of the digest to a hexadecimal string | ||
| // not sure if this is correct, padding each byte as 2 characters | ||
| let hex_str: String = result.iter().fold(String::new(), |mut acc, byte| { | ||
| let _ = write!(acc, "{:02x}", byte); | ||
| acc | ||
| })[..15] | ||
| .to_string(); | ||
| let hash_val = u64::from_str_radix(&hex_str, 16).unwrap(); | ||
|
|
||
| hash_val as f64 / LONG_SCALE as f64 | ||
| } | ||
|
|
||
| pub fn get_matching_variant(&self, feature_flag: &FeatureFlag) -> Option<String> { | ||
| let hash = self.get_hash(feature_flag, "variant"); | ||
| let mut total_percentage = 0.0; | ||
|
|
||
| for variant in feature_flag.get_variants() { | ||
| total_percentage += variant.rollout_percentage / 100.0; | ||
| if hash < total_percentage { | ||
| return Some(variant.key.clone()); | ||
| } | ||
| } | ||
| None | ||
| } | ||
| } |
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